The present invention relates to a culture skin and a process for preparing the same. More particularly, the present invention relates to a culture skin matrix, a culture skin and processes for preparing the same for reconstructing or healing a defect tissue in an early stage by applying the matrix or the skin to a skin defect such as a burn, a wound, a decubitus or a skin ulcer.
Hitherto a medical treatment used in general as therapy for a skin defect reaching to an upper layer of dermis such as a superficial dermal burn is a cover of the skin defect with wound dressings, ointment gauze or the like. However, when there is caused a skin defect reaching to a lower layer of dermis such as a deep dermal burn, a dermal burn or a decubitus in at least the second grade, self-reconstruction in a cutaneous tissue by proliferation of epidermal cells can not be expected. Therefore, such a defect has been treated by debriding a slough or an abnormal granulation tissue, reconstructing a normal granulation tissue by covering the defect with an allogenic skin, wound dressings or the like, and then reconstructing a skin by performing autologous split-thickness skin graft. In case of performing the autologous split-thickness skin graft, however, because a skin is taken from a normal position of a patient, there arises a problem as to restoration of appearance that the scar remain at the position. Further, in case that a wound extends in a wide range, it is difficult to carry out the autologous split-thickness skin graft.
In order to solve the problem, there have been developed a technique wherein epidermal cells or fibroblasts are taken from a small skin piece and mass-cultured in a culture flask, and various culture skins using these cultured cells.
The culture epidermis developed by Howard Green, James G. Rheinwald et al. is obtained by taking a skin of postage stamp size and mass-culturing cells derived from the skin in a culture flask to give an epidermal sheet. As to the sheet, the problem has been pointed out that taking ratio in autologous skin graft is low because basal cells being the most important cells are damaged by enzyme treatment in case of removing the sheet from the flask (see Yoshimitsu Kuroyanagi, Seitaizairyo (Biomaterial) 9, February, 1991).
Also, Eugene Bell et al. (see Science, 211, pages 1052-1054, 1981) developed a culture skin by mass-culturing each of epidermal cells and fibroblasts in a culture flask which were obtained by separating them from a skin, and stratifying epidermal cells on a collagen gel into which fibroblasts has been incorporated to give a culture skin. However, there was a fault that a collagen gel extremely contracts during cell culture.
Further, Steven Boyce et al. (see SURGERY, 103, pages 421-431, April, 1988) developed a culture skin by mass-culturing epidermal cells obtained from a skin and stratifying the epidermal cells on a matrix in a form of sponge which was obtained by adding a small amount of chondroitin-6-sulfate to collagen.
Also, culture skins having atelocollagen as a matrix are described in Japanese Unexamined Patent Publications No. 246371/1987 and No. 332561/1992. In Japanese Unexamined Patent Publication No. 246371/1987, a culture skin having an atelocollagen sheet as a matrix is described. In the above culture skin, however, there was a problem that taking ratio of epidermis is low in autologous skin graft. The reason is that the sheet has no penetrating pore, and nutrition being indispensable to cell proliferation and the like and being given from a covered wound face is hardly supplied through the sheet to epidermal cells on the opposite side of the sheet.
Also, in case of preparing a culture skin wherein only fibroblasts are taken into the skin, nutrition to be supplied from a covered wound face is hardly supplied throughout the culture skin. Therefore, proliferation and metabolism of fibroblasts are harmfully influenced and release of biologically active substances (e.g., growth factors, cytokines and the like) is not performed without hitch. These and the like often interfere with reconstruction of skin or good granulation.
There was the problem that a wound becomes a hotbed of infection by reason that exudate was excessively pooled in a wound and discharge of the exudate is not carried out properly, because of no penetrating pore.
In Japanese Unexamined Patent Publication No. 332561/1992, an atelocollagen sponge is described which is provided with a penetrating pore on purpose to solve the problem as described above. In case of providing the sponge with a penetrating pore, cells are flowed out through the pore and lost in being seeded. Therefore, pre-coating of the sponge with atelocollagen gel or the like before cell seeding is essential to the gel in order to compensate for such faults. There is the problem that such coating method is not only complicated but also expensive from the view points of cost for preparation of a culture skin. Therefore, development for more inexpensive and more simple alternative culture skin or preparation technique thereof has been desired.
The problems to be solved hitherto in a culture skin using collagen as a matrix were as follows:
1. contraction of a culture skin in cell culturing,
2. the problem that nutrition supply throughout cultured cells from a covered wound face is not smooth, because a culture skin matrix becomes a barrier after covering a defect tissue of a skin with a culture skin,
3. the problem that exudate is excessively pooled in a position where a defect tissue of a skin is covered with a culture skin after the covering, and
4. the problem that cells flow out through a pore and are lost when being seeded, in the case a matrix is provided with a when penetrating pore in order to solve the above-mentioned points 2 and 3.
The present invention is made in order to solve the above points 1-4.
An object of the invention is to provide a culture skin for reconstructing or healing a defect tissue of a skin in an early stage by applying the culture skin to a skin defect such as a burn, a wound, a decubitus or a skin ulcer. More particularly, the object of the invention is to provide a culture skin which has a function by which there can be smoothly carried out nutrition supply from a covered wound face to cells of the culture skin and discharge of the exudate being excessively pooled in a wound, and is obtainable at a low cost without causing contraction.
A further object of the invention is to provide a culture skin matrix which can be used in the above-mentioned culture skin as a matrix.
A still further object of the invention is to provide processes for preparing the culture skin and the culture skin matrix.
These and other objects of the present invention will become apparent from the description hereinafter.